A Grounding challenge , please help.. - Page 3 - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 24th February 2011, 01:07 AM   #21
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Blog Entries: 22
Quote:
Originally Posted by johnferrier View Post
Stupid question ?

What do diodes 2, 3, 5, & 6 do ? (The four shorted A to K.) I've seen this before with bridge circuits. What am I missing ? ? ??

.
Not a stupid question at all The BYV32E's are a dual diode in a 3 pin TO220 package. the cathodes share a common pin but the annodes have separate pins. I used three for each bridge and the extra diodes in the packages where I was only using one of the diodes I shorted to reduce the possibility that they could pick up noise if I left one end floating I grabbed the image from my blog page and without the text that went along with it it doesn't make a whole lot of sense!

The PS I'm working on at the moment I'm going to use 4 X BYV32E's and wire the two diodes in parallel in each package... I wasn't sure if this was a good idea when I did the one you have shown the image for, but I'm getting more adventurous

Reason I showed them on the schematic was because I was using expresspcb to do the layout for my verroboard, and having the actual components accurately represented allowed me to use the netlist to check the board layout against the circuit... probably overkill for such a simple circuit but nice to check

Tony.
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos

Last edited by wintermute; 24th February 2011 at 01:13 AM.
  Reply With Quote
Old 24th February 2011, 01:11 AM   #22
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Blog Entries: 22
Elbert, have to be quick, my lunch hour is over. I used lead simply because I could easily shape it (and solder it), and it was available in sheets at the local hardware shop. I figured that since it was dense it should block EMI well. I didn't try any other materials.

I thought about mentioning putting a piece of steel (it looks like your bulkhead is aluminium?) in between but JCX beat me to it

Tony.
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos
  Reply With Quote
Old 24th February 2011, 09:52 AM   #23
Elbert is offline Elbert  Norway
diyAudio Member
 
Join Date: Mar 2008
Makes sense to use lead from a practical point of view then in terms of cutting and shaping.

Lead is not a particularily good conductor, (as far as metalls go), so a better conducting material should in theory have been more optimum for shielding electric field.

Allso, lead has a verty low magnetic permeability, i,e, magnetic flux lines will not seek to flow through it, thus it is not a suitable magnetic shield either.

Perhaps there are some other properties that makes lead suitable?
Or perhaps it was just good enough for your applications?

Annyway, off to get some mild steel sheet here!
  Reply With Quote
Old 24th February 2011, 10:02 AM   #24
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Sorry if this has already been covered, but you do realise that if you connect two rectifier bridges to one secondary you have effectively lost all control of PSU grounding? This may not show up in a simulation, as that will assume that all diodes and all capacitors are identical. You can just about get away with this provided the two DC supplies are used for isolated circuits with no other connections between them (except via transformers or opto-isolators). You can ground either of the two PSU 'grounds', but the other one will then become dirty - you can't ground both of them.
  Reply With Quote
Old 24th February 2011, 10:41 AM   #25
diyAudio Member
 
abraxalito's Avatar
 
Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Blog Entries: 105
Send a message via MSN to abraxalito Send a message via Yahoo to abraxalito Send a message via Skype™ to abraxalito
Quote:
Originally Posted by Elbert View Post
Lead is not a particularily good conductor, (as far as metalls go), so a better conducting material should in theory have been more optimum for shielding electric field.
Yes but the troublesome fields from transformers are nearly always the magnetic ones, not the electric.

Quote:
Allso, lead has a verty low magnetic permeability, i,e, magnetic flux lines will not seek to flow through it, thus it is not a suitable magnetic shield either.
That is true for a DC magnetic field - like might come from a permanent magnet. However here with an AC field there's another way to shield - by eddy current effects. That's the reason lead is working to a degree - but steel would be far better because of its higher permeability, meaning the skin depth is shallower. Oh and steel is more conductive than lead, so better still.


Quote:
Annyway, off to get some mild steel sheet here!
Excellent
__________________
I have the advantage of having found out how hard it is to get to really know something... how easy it is to make mistakes and fool yourself. - Richard Feynman
  Reply With Quote
Old 24th February 2011, 10:45 AM   #26
Elbert is offline Elbert  Norway
diyAudio Member
 
Join Date: Mar 2008
Quote:
Originally Posted by DF96 View Post
Sorry if this has already been covered, but you do realise that if you connect two rectifier bridges to one secondary you have effectively lost all control of PSU grounding? This may not show up in a simulation, as that will assume that all diodes and all capacitors are identical. You can just about get away with this provided the two DC supplies are used for isolated circuits with no other connections between them (except via transformers or opto-isolators). You can ground either of the two PSU 'grounds', but the other one will then become dirty - you can't ground both of them.
Yes, this actually occured to me at one point. That is why I connected the PSU grounds together at the reservoir capacitors!

So, steel plate shielding it is..

Looks like it is going to be very tricky for me to enclose the Toroid, so I'll go for placing steel sheet between the toroid and the x-over card..

But what would be the better strategy?

One thick plate of steel or several thinner sheets stacked? Or is it only a matter of thickness irrespective of sheets/ layers?

Last edited by Elbert; 24th February 2011 at 10:50 AM.
  Reply With Quote
Old 24th February 2011, 10:48 AM   #27
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Blog Entries: 22
Hi Elbert I did a bit of a google search on lead as a shield and yes your points are very valid, I probably would have been better off with a steel cylinder roughly the size of the traffo possibly even a tin can(if big enough) would work! I did it probably at least 10 years ago (possibly even 15 years ago) the amp is 24 years old and googling wasn't a natural action back then I knew nothing about EMF/EMI and just figured that lead being dense should block it well (I'd determined it was radiation by moving the transformer outside the chasis which reduced the noise to almost nothing).

The lead definitely makes quite a difference, though I never did any tests with a mic to quantify the absolute difference in noise levels. Perhaps the sheer density of the lead works to block rather than dissipate the EMF... I don't really know, though after what I read today mild steel is probably a better choice!

Tony.
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos
  Reply With Quote
Old 24th February 2011, 11:04 AM   #28
Elbert is offline Elbert  Norway
diyAudio Member
 
Join Date: Mar 2008
Yes, sometimes we just have to fix something, and sometimes it just works!

As you say, from available information, there seems to be better candidates than lead when considering the electrical and magnetic properties.

The shielding properties of lead is of course most relevant with respect to radioactive radiation like high-energy electrons (Beta-radiation) and gamma and x-rays, mainly due to the high density of lead, but I've found no information that the properties making lead effective for these high energy forms of radiation could have any effect on low frequency and low density electro-magnetic radiation.
That would be cool though, but I guess we are talking about two very different domains of physics!
  Reply With Quote
Old 24th February 2011, 11:10 AM   #29
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Quote:
Yes, this actually occured to me at one point. That is why I connected the PSU grounds together at the reservoir capacitors!
OK, that wasn't clear from the diagrams. This issues catches some people out, especially as simulations don't show it.

Lead will be fine, but unnecessarily heavy, for electrostatic shielding but useless for magnetic shielding as it is not ferromagnetic and is a poor conductor. You need mu-metal for that.
  Reply With Quote
Old 24th February 2011, 11:26 AM   #30
Elbert is offline Elbert  Norway
diyAudio Member
 
Join Date: Mar 2008
My mistake, the diagram I posted showed the PSU layout as it was BEFORE I modified it and connected the ground points together!

But thanks for taking an interrest and making the observation nevertheless!

Mu-metall seems to be very effective, but unfortunately, it is rather expensive.

This is why I'll throw in some steel sheet to see if that can get rid of the worst so my last precious strip of mu-metal doesn't get overloaded and saturated!
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Here is a Challenge latala Solid State 41 12th May 2011 01:13 AM
Lions and Tigers and Grounding Problems, Oh My! DoZ Grounding... EchoWars Solid State 37 3rd August 2008 08:50 AM
LM3875 kit grounding, optimal grounding for separate amps and psu? findog Chip Amps 9 16th May 2005 09:27 PM
a challenge --or I need help lawrence99 Car Audio 0 9th March 2005 04:44 AM
The challenge ! thylantyr Solid State 51 24th July 2003 08:41 PM


New To Site? Need Help?

All times are GMT. The time now is 11:13 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2